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Seminar for City of Tomorrow

 

‣ Theme: High Pressure Synchrotron X-ray Diffraction Study of Calcium Silicate Hydrates

 

‣ Date/Time: 10:00, August 3, 2009

 

‣ Place: KAIST W16 (#307)

 

‣ Lecture: Jae Eun Oh(Dept. of Civil and Environmental Eng. UC Berkeley)

 

* Professors and students from other departments will always be welcomed.

* For further information please, contact Eun-Ae Park, Sang-Phil, Park in KIUSS

* Phone) 042-350-4467, 4541 e-mail) lady9764@kaist.ac.kr

 

‣ Abstract

Since Portland cement was patented by Joseph Aspdin in 1824, its use has grown until it is now ubiquitous in construction projects. The manufacturing and processing of ordinary Portland-cement concrete (OPC) consists of about 12% cement, 8% mixing water, 80% aggregate by mass, and, in some cases, chemical admixtures. Although concrete is an extremely versatile material, it suffers a few major critical drawbacks.

Firstly, it annually consumes up tremendous amount of natural resources. The world consumes 1.5 billion tons of Portland cement, 9 billion tons of sand and rock with one billion tons of drinkable water, which is 110,000 times of the volume of potable water larger than the sea water contained in the San Francisco Bay, resulting in production of 17 billions tons of structural concrete per year. No materials can be comparable among consumptions by human except for water.

Secondly, the cement production yields 1.7 billion tons of huge CO2 emission, which is taking up at least 5-7% of world-wide man-made CO2. Generally, one tone of cement production generates nearly one tone of CO2 emission.

Thirdly, the aging of civil infrastructure made of concrete became a serious economical problem. The service life of concrete structures such as dams, buildings, bridges, roads is largely reduced by corrosion, frost action, sulfate attack and alkali-silica reaction. The present status of cement production and decaying infrastructure is not sustainable.

To resolve these problems, two significant achievements must be prerequisite such as the following: (1) largely enhancing essential mechanical properties of concrete, resulting in considerable reduction of consumption of concrete for an equivalent degree of construction purpose; and (2) fully understanding of the mechanism of concrete deterioration, leading to development of proper repair strategies. However, traditional approaches based on macro-scale of concrete researches have already faced the limit in resolving these problems because most of overall material behaviors are governed by micro and nano-scale of materials properties. At present, further inherent solutions can be made only by nano- and micro-scale of studies. Therefore, nano-scale of research should be accompanied with the traditional macro-scale of approaches.

Calcium silicate hydrate (C-S-H) is the most important chemical reaction product of Portland cement hydration with water because C-S-H are mainly responsible for the mechanical properties of fully hydrated cement paste with taking up 50~60% in volume of fully hydrated cement paste. Thus, there are great benefits to characterize and improve the mechanical properties of C-S-H to achieve optimized sustainable concrete with lower cement consumption. Unfortunately, the crystal structure and intrinsic mechanical behavior of C-S-H in a nano-scale length was not well understood because C-S-H is extremely complex material so that it has been one of the most difficult issues in the academic world. Because of its highly amorphous nature, even its fundamental material properties –- such as bulk modulus as well as its crystal structure - have not been well characterized although we have used Portland cement over 180 years. Therefore, instead, rare natural mineral 14Å tobermorite and synthetic C-S-H (I) have been extensively studied as analogues of C-S-H because of their close similarities of crystal structures to C-S-H.

In the present study, using a high pressure synchrotron X-ray diffraction technique at beamline 12.2.2 of Advance Light Source (ALS) in Lawrence Berkeley National Laboratory, for the first time, the bulk moduli and its equations of state are experimentally obtained for several essential C-S-Hs such as follows: (1) tobermorite 14Å, 11Å and 9Å; (2) synthetic C-S-H (I); (3) Alkali-activated slag based C-S-H (I). Particularly, the result on the tobermorites has a great significance in cement and concrete researches. These results are essential in understanding the inherent nano-crystal structure determining the mechanical properties of calcium silicate hydrate and also can be used as inherent material parameters in developing a simulation package for the mechanical behavior of concrete structure.


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